Generally whilst we state that there is no upgrade path generally you can upgrade between releases fine. Especially on test sites. The differences occur for example during alpha1 and beta1 we introduced a new plugin for the new google recaptcha. At beta 2 we then removed it again and merged it with the existing plugin. That meant if you upgraded you would still have the plugin installed but it would not be maintained etc. The same goes for new files added and removed during the release period (and obviously we don't guarantee the security of said files - although we try and ensure they are as good as possible).
Since 3.2.2 we can have multiple database files per release so you database schema should always stay upto date (which used to be the major issue with upgrade paths).
In summary you should never upgrade live sites or base them on non-stable releases for the reason I listed in the first paragraph but for a straightforward testing site you should be fine just upgrading as usual via the Joomla upgrade component :)
On a personal note if it's just from 3.4 RC to live then I can tell you (as I released both) that there are none of the above issues from RC to the stable release. A very low number of changes were made between the RC and the stable release.
